Heat transfer enhancement for a condensing furnace

ABSTRACT

A heat exchanger is provided including a plurality of heat exchanger tubes. A first fluid flows through each heat exchanger tube and a second fluid flows around an exterior of each heat exchanger tube. A turbulator is disposed within at least one of the heat exchanger tubes. The turbulator extends at least a portion of the length of the heat exchanger tube. The turbulator includes a generally flat sheet of material having a plurality of integrally formed turbulence generating elements. The turbulence generating elements extend from a plane of the sheet of material into the first fluid flow. A disturbance is created in the first fluid flow adjacent each turbulence generating element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/712,335, filed on Oct. 11, 2012, the entire contents of which are incorporated herein by reference and claims the benefit of U.S. Provisional Patent Application Ser. No. 61/818,948, filed on May 3, 2013, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates generally to gas-fired condensing furnaces, and more particularly, to a turbulator used in a secondary or condensing heat exchanger of such gas-fired condensing furnaces.

Conventional high efficiency condensing furnaces commonly include a secondary or condensing heat exchanger configured to extract additional heat from the hot heating fluid by condensing a portion of the water vapor formed during the combustion of fuel and air. Typically, round tube plate fin type heat exchangers are used as the condensing heat exchanger. In a round tube plate fin type heat exchanger, the heated air flows across the finned exterior of the tubes, while the combustion products flow through the interior of the tubes, typically in a cross-wise orientation. In applying round tube plate fin heat exchanger technology to furnaces for heating air, a large disparity in heat transfer coefficients may occur between the air side and the flue side of the heat exchanger. In the condensing heat exchanger, the thermal resistance of the flue side may be between 80-90% of the overall resistance. The air side thermal resistance is generally much lower because of the relatively large flow rate of heated air, and the finned heat transfer surface area. However, the flue side does not effectively transfer heat because the flow rate is significantly lower and because the surface area is limited to the interior wall of the tube. The flue side flow regime is generally either laminar or transitional and has an average Reynolds number in the range of about 2,000 to about 4,000. Consequently, the overall rate of heat transfer is fundamentally limited by the flue side thermal resistance.

In a bare tube, the convection heat transfer coefficient and the heat transfer rate are highly dependent upon the thickness and characteristics of the boundary layer. Because the thermal boundary layer thickness is zero at the tube entrance, the convection heat transfer coefficient is extremely large in this inlet region. However, the convection heat transfer coefficient decays rapidly as the thermal boundary layer develops, until a constant value associated with a fully developed boundary layer is reached. Due to the development of the thermal boundary layer and insufficient radial mixing, a large temperature gradient occurs between the bulk fluid near the central axis and the tube wall. As a result, the in-tube heat transfer performance is inherently limited. As is known in the art, a turbulator may be installed in a heat exchanger tube to minimize boundary layer effects, promote mixing, and improve heat transfer. In general, a turbulator is a bent strip of metal inserted into the tube, such that gas passing there through will be variously deflected in an attempt to break up the boundary layer, reduce temperature gradients and improve the convection heat transfer coefficient. The inclusion of a turbulator, however, causes an additional flue side pressure drop and also adds manufacturing cost.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment of the invention, a heat exchanger is provided including a plurality of heat exchanger cells. A first fluid flows through each heat exchanger cell and a second fluid flows around an exterior of each heat exchanger cell. A turbulator is disposed within at least one of the heat exchanger cells. The turbulator extends at least a portion of the length of the heat exchanger cell. The turbulator includes a generally flat sheet of material having a plurality of integrally formed turbulence generating elements. The turbulence generating elements extend from a plane of the sheet of material into the first fluid flow. A disturbance is created in the first fluid flow adjacent each turbulence generating element.

According to another embodiment, a condensing furnace includes a heat exchanger having an inlet and an outlet, wherein a first fluid flows through the heat exchanger and a second fluid flows around an exterior of the heat exchanger; and a turbulator positioned within the heat exchanger, the turbulator extending at least a portion of a length of the heat exchanger, the turbulator including: a generally flat rectangular sheet; and a plurality of turbulence generating elements formed integrally with the rectangular sheet and extending from a plane of the rectangular sheet into the first fluid flow, such that a disturbance is created in the first fluid flow adjacent each turbulence generating element.

According to another embodiment, a heat exchanger includes a plurality of heat exchanger tubes, wherein a first fluid flows through each heat exchanger tube and a second fluid flows around an exterior of each heat exchanger tube; and a turbulator disposed in one of the heat exchanger tubes and extending at least a portion of a length of the heat exchanger tube, the turbulator including a generally flat sheet of material having a substantially non-linear contour configured to interrupt a flow of the first fluid through the heat exchanger tube.

According to another embodiment, a condensing furnace includes a heat exchanger having an inlet and an outlet, wherein a first fluid flows through the heat exchanger and a second fluid flows around an exterior of the heat exchanger; and a turbulator positioned within the heat exchanger, the turbulator extending at least a portion of a length of the heat exchanger, the turbulator including a generally flat sheet of material having a substantially non-linear contour configured to interrupt a flow of the first fluid through the heat exchanger tube.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view, partially broken away, of an exemplary condensing furnace;

FIG. 2 is an exploded, perspective view of an exemplary heat exchanger assembly used in a condensing furnace;

FIG. 3 is a perspective view of a turbulator for use in a heat exchanger according to an embodiment of the invention;

FIG. 4 is a top view of a turbulator for use in a heat exchanger according to an embodiment of the invention;

FIG. 5 is a side view of a turbulator for use in a heat exchanger according to an embodiment of the invention;

FIG. 6 is a top view of a turbulator for use in a heat exchanger according to an another embodiment of the invention;

FIG. 7 is a side view of a turbulator for use in a heat exchanger according to an another embodiment of the invention;

FIG. 8 is a top view of a turbulator for use in a heat exchanger according to an another embodiment of the invention;

FIG. 9 is a side view of a turbulator for use in a heat exchanger according to an another embodiment of the invention;

FIG. 10 is a perspective view of a turbulator according to another embodiment of the invention;

FIG. 11 is a perspective view of a turbulator according to another embodiment of the invention;

FIG. 12 is a perspective view of a turbulator according to another embodiment of the invention;

FIG. 13 is a perspective view of a turbulator according to another embodiment of the invention;

FIG. 14 is a top view of a turbulator according to another embodiment of the invention;

FIG. 15 is a top view of a turbulator according to another embodiment of the invention;

FIG. 16 is a top view of a turbulator according to another embodiment of the invention;

FIG. 17 is a perspective view of a heat exchanger and a turbulator mounted within the heat exchanger according to an embodiment of the invention;

FIG. 18 is a perspective view of a heat exchanger and a turbulator mounted within the heat exchanger according to another embodiment of the invention;

FIG. 19 is an end view of a heat exchanger and a turbulator mounted within the heat exchanger according to another embodiment of the invention; and

FIG. 20 is a perspective view of a turbulator mounted within the heat exchanger according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a condensing furnace 10 is illustrated. The condensing furnace 10 includes a cabinet 11 housing therein a burner assembly 14, primary heat exchanger 12, condensing heat exchanger assembly 18, induced draft motor assembly 20, and circulating air blower 22. The furnace 10 includes a vertical arrangement of the above major assemblies, and particularly the heat exchanger assembly 12 and circulating air blower 22 in order to establish conditions to provide additional heat transfer and improve overall furnace efficiency by producing condensation in the condensing heat exchanger assembly 18.

Burner assembly 14 includes a plurality of inshot burners 15, one for each respective primary heat exchanger cell 17. Burners 15 receive fuel gas from the gas control assembly (not shown) and inject the fuel gas into respective primary heat exchanger inlets 24. A part of the injection process includes drawing air into primary heat exchanger assembly 12 so that the fuel gas and air mixture may be combusted therein. It should be understood that the number of primary heat exchanger cells 17 and corresponding burners 15 is established by the required heating capacity of the furnace 10 and may vary.

Now referring to FIG. 2, each primary heat exchanger cell 17 has a serpentine flow path which connects the primary heat exchanger inlets 24 in fluid communication to respective primary heat exchanger outlets 26. As the combustion gas exits the primary heat exchanger outlet 26, it flows into coupling box 16. Also connected to the coupling box 16 and in fluid communication therewith is secondary or condensing heat exchanger assembly 18 including a plurality of interconnected condensing heat exchanger tubes 52. Though the illustrated heat exchanger tubes 52 have a substantially circular cross-section, alternate configurations, for example having a rectangular or oval cross-section, are within the scope of the invention.

Each secondary or condensing heat exchanger tube 52 includes a respective condensing heat exchanger inlet 54 opening into coupling box 16 and a condensing heat exchanger outlet 56 opening into condensate collector (not shown) through apertures in mounting panel 60. Condenser heat exchanger outlets 56 deliver heating fluid exhaust, for example flue gases and condensate, to the condensate collector (not shown). Further, there are a predetermined number of condensing heat exchanger tubes 52 for each primary heat exchanger cell 17, defined by the required furnace efficiency, flue side hydraulic resistance, air side hydraulic resistance, and combustion product mixture composition.

The induced draft motor assembly 20 (see FIG. 1) includes a motor with an inducer wheel (not shown) for drawing the heating fluid created by burner assembly 14 through primary heat exchanger assembly 12, coupling box 16, and condensing heat exchanger assembly 18, and thereafter exhausting the heating fluid to a flue duct (not shown). A circulating air blower 22 delivers return air, from the enclosure or space to be heated, in a flow direction generally perpendicular to the flow of the combustion fluid through secondary heat exchanger assembly 18 and primary heat exchanger 12. The cooler return air passing over the condensing heat exchanger assembly 18 lowers the temperature of the heating fluid. This reduction in temperature of the heating fluid below the dew point causes a portion of the water vapor therein to condense, thereby recovering sensible and latent heat energy. The condensate formed within each individual secondary heat exchanger tube 52 flows out of outlet 56 through condensate collector (not shown). As blower 22 continues to force air to be heated over the outside of the secondary heat exchanger 18 and the primary heat exchanger 12, heat energy is transferred from the heating fluid within the secondary and primary heat exchangers 18, 12 to the return air.

Referring now to FIGS. 3-10, an exemplary turbulator 100 is illustrated for use within a heat exchanger tube 52. In one embodiment, a first end 102 of the turbulator 100 may be mounted adjacent the inlet 54 of the heat exchanger tube 52 and the second, opposite end 104 may be fixed adjacent the outlet end 56 of the heat exchanger tube 52 such that the turbulator 100 extends the full length of the heat exchanger tube 52. Alternatively, the turbulator 100 may extend over only a portion of the length of the heat exchanger tube 52. In one embodiment, the turbulator 100 is formed from an elongated, generally flat, rectangular sheet 106, such as a piece of sheet metal for example and includes a plurality of turbulence generating elements 110 extending out of the plane of the rectangular sheet 106. The plurality of turbulence generating elements 110 may extend from the plane of the rectangular sheet 106 in the same direction. Alternatively, at least one turbulence generating element 110 may extend out of the plane of the rectangular sheet 106 in a first direction, and at least one turbulence generating element 110 may extend out of the plane of the rectangular sheet 106 in a second, opposite direction.

These turbulence generating elements 110, also referred to as winglets, are formed, in particular, by means of a deforming production process, including stamping, punching, or embossing. A portion of each turbulence generating element 110, for example an edge, remains connected to the rectangular sheet 106. These turbulence generating elements 110 improve the transfer of heat between the heating fluid flowing through the interior of the heat exchanger tube 52 and the air flowing around the exterior of heat exchanger tube 52 by generating disturbances, such as vortices for example, in the fluid flowing inside the heat exchanger tube 52.

The turbulence generating elements 110 may be any shape including but not limited to triangular, oval, square, and rectangular for example. In one embodiment, illustrated in FIG. 11, the turbulence generating elements 110 include a generally curved surface, such that the turbulence generating elements 110 have a semi-circular cross-section for example. The curved surface may be oriented perpendicular or parallel to the length of the turbulator 100. In another embodiment, illustrated in FIG. 3, the turbulence generating elements 110 are generally triangular in shape. As illustrated in FIGS. 3-7, the triangular turbulence generating elements 110 may be right triangles connected to the rectangular sheet 106 along the hypotenuse. The plurality of turbulence generating elements 110 may be uniform along the length of the turbulator 100, or alternatively, the turbulator 100 may include turbulence generating elements 110 having various sizes and/or shapes.

Referring now to FIGS. 4 and 5, the turbulence generating elements 110 are formed such that each turbulence generating element 110 has a width W and a length L. The width W and length L need not be uniform across the plurality of turbulence generating elements 110. The width of a portion of the turbulence generating elements 110 may be about half the width of the rectangular sheet 106 that forms the turbulator 100. The width W of the turbulence generating elements 110 may be in the range of about 4 mm to about 25 mm. In one embodiment, the width W of a portion of a turbulence generating element 110 is about 5.5 mm. The turbulence generating elements 110 may be disposed in the center of the rectangular sheet 106 such that about ½ W is disposed between each side of the turbulence generating element 110 and the sides of the rectangular sheet 106. The turbulence generating elements 110 may have a length L to width W ratio (L/W), also referred to as a chord ratio, in the range of about 1 to about 5. In one embodiment, the chord ratio of the turbulence generating elements 110 is about 2.

A pitch P extends between a first point on a first turbulence generating element 110 and a second point on a second turbulence generating element 110. The first point and the second point are the same relative point for adjacent turbulence generating elements 110 extending from the plane of the rectangular sheet 106 in the same first direction. A same side pitch ratio (P/W) for adjacent turbulence generating elements 110 extending out of the plane of the rectangular sheet 106 in a first direction is in the range of about 5 to about 100. A distance X is defined between an edge of a turbulence generating element 110 extending from the plane of the rectangular sheet 106 in the first direction and an adjacent edge of a turbulence generating element 110 extending from the plane of the rectangular sheet 106 in the opposite direction. In the case of oppositely directed turbulence generating elements 110 lying immediately one after the other, the distance X may approach 0. An opposite side pitch ratio (X/W) is in the range of about 0 to about 50. In one embodiment, the opposite side pitch ratio is about 40. Each turbulence generating element 110 is arranged at an approach angle θ relative to an airstream velocity vector. The approach angle is defined as the angle between the chord line of the wing or winglet turbulator and the freestream velocity vector. The approach angle θ may be in the range of about 10° to about 90°. In one embodiment, the approach angle is about 27°. The inclination angle of the winglet is defined as the angle between the plane of the turbulence generating element 110 and the plane of the rectangular sheet 106. Furthermore, the inclination angle of the turbulence generating elements 110 in relation to the plane of the rectangular sheet 106 may be 90°. Alternatively, at least a portion of at least one turbulence generating element 110 may have an inclination angle in relation to the plane of the rectangular sheet 106 other than 90°, for instance between 15° and 65°.

Consecutive turbulence generating elements 110 extending from the plane of the rectangular sheet 106 in either the same direction or the opposite direction may be oriented uniformly in a single direction, for instance facing the flow, as shown in FIG. 4. The turbulence generating element 110 configuration shown in FIGS. 4 and 5 creates similarly rotating vortices in the heating fluid flow within a heat exchanger tube 52. The intensity of these co-rotating vortices is reinforced at each turbulence generating element 110 along the flow direction of the turbulator 100, thereby maximizing the intensity of each vortex. Alternatively, at least one of the turbulence generating elements 110 may be rotated about a longitudinal axis of the rectangular sheet parallel to the flow direction (see FIG. 6). In one embodiment, at least one of the turbulence generating elements 110 is rotated 180 degrees relative to the remainder of the plurality of turbulence generating elements 110. The vortices created by turbulence generating elements 110 rotated about the longitudinal axis rotate in different directions. In such configurations, the self-sustaining intensity of each vortex is reduced, but additional flow mixing is generated.

As illustrated in FIG. 8, at least one of the turbulence generating elements 110 may be oriented in direction opposite the flow through the heat exchanger tube 52 (see FIG. 8). To orient one or more turbulence generating element 110 in a direction opposite the flow, the turbulence generating element 110 is rotated about a lateral axis of the rectangular sheet 106, perpendicular to the flow. In one embodiment, the at least one turbulence generating element 110 is rotated 180 degrees about the lateral axis. As shown in FIG. 8, the triangular turbulence generating element 110 facing opposite the flow is not oriented to produce maximum vortex generation, but the vortex is insensitive to flow direction. In addition, consecutive turbulence generating elements 110 may be rotated about both a longitudinal axis and a lateral axis relative to an adjacent turbulence generating element 110.

The turbulator 100 may include a single row of turbulence generating elements 110 generally aligned about a longitudinal axis, such as central axis A for example. Alternatively, consecutive turbulence generating elements 110 may be positioned on alternating sides of a longitudinal axis. In some embodiments, more than one turbulence generating element 110 is located at a longitudinal position of the turbulator 100 (FIG. 10). If multiple turbulence generating elements 110 are arranged at a single longitudinal position of the turbulator 100, those turbulence generating elements 110 may be identical or alternatively may vary in size, shape, and orientation. In one embodiment, a first and second turbulence generating element 110 are arranged symmetrically about a central axis A at a first longitudinal position of the turbulator 100.

In another embodiment, illustrated in FIGS. 12-14, the turbulator 200 may be formed from an elongated, generally flat piece of material having a substantially non-linear contour such that the turbulator 200 has a zig-zag shape formed by a plurality of opposing turns 208. The contour of the zig-zag sheet 206 may be generally smooth such that the turns 208 are rounded (FIG. 12), or the contour may be disjointed such that the turns 208 are generally angular (FIG. 13). In embodiments where the turns 208 of the zig-zag sheet 206 are angular, the zig-zag sheet 206 is formed from a plurality of generally linear sections 220 connected to one another by a plurality of angled sections 222 (FIG. 14). Each successive angled section 222 is oriented in a direction from the longitudinal axis opposite the direction of the preceding angled section 222. The linear sections 220 are substantially identical and have a length L1 parallel to the longitudinal axis of the zig-zag sheet 206, and a width W1 perpendicular to the longitudinal axis of the zig-zag sheet 206. The width W1 may be in the range of about 4 mm to about 25 mm, and in one embodiment, may be approximately 5.5 mm. Each of the angled sections 222 has a length L2, parallel to the longitudinal axis, and is arranged at a skew angle A1 to the longitudinal axis. The skew angle A1 may be between about 15 degrees and about 60 degrees, and in one embodiment is about 45 degrees.

A length ratio (L2/W1) of each angled section 222 is generally in the range of about 0.5 and about 5, and in one embodiment, the angled sections 222 of the zig-zag sheet 206 have a length ratio of about 1. A length ratio (L1/W1) of each linear section 220 is generally in the range of about 1 to about 10. In one embodiment, the linear section 220 of the zig-zag sheet 206 generally have a length ratio of about 2. The transverse width W2 of the turbulator 200 is defined as the distance between the two parallel lines bounding the outermost edges of the zig-zag sheet 206. The transverse width ratio (W2/W1) of the turbulator 200 is in the range of about 1.5 to about 5, and in one embodiment the transverse width ratio (W2/W1) is about 2.

Each of the plurality of turns 208 of the zig-zag sheet 206 may include one or more turbulence generating elements 210, as illustrated by dashed lines in FIG. 14. The plurality of turbulence generating elements 210 may extend from the plane of the zig-zag sheet 206 in the same direction, or alternatively, at least one turbulence generating element 210 may extend out of the plane of the zig-zag sheet 206 in a first direction, and at least one turbulence generating element 210 may extend out of the plane of the zig-zag sheet 206 in a second, opposite direction (FIG. 15). In one embodiment, the turbulence generating elements 210 are integrally formed with the turbulator zig-zag sheet 206 by bending a portion of a turn 208, such as a corner for example, out of the plane of the zig-zag sheet 206 (FIG. 14).

As previously disclosed, the turbulence generating elements 210 are formed such that each turbulence generating element 210 has a width W and a length L. The width and length L need not be uniform for each of the pluarlity of turbulence generating elements 210 of the turbulator 200. In one embodiment, the width W of at least one turbulence generating element 210 is substantially equal to the width W1 of a linear section 220 and the length of at least one turbulence generating element 210 is about twice the width (2W). The turbulence generating elements 210 may have a length L to width W ratio (L/W), also referred to as a chord ratio, in the range of about 1 to about 5. In one embodiment, the chord ratio of the turbulence generating elements 210 is about 2.

A same side pitch ratio (P/W) for adjacent turbulence generating elements 210 extending out of the plane of the zig-zag sheet 206 in a first direction is in the range of about 2 to about 100. A distance X is defined between an edge of a turbulence generating element 210 extending from the plane of the zig-zag sheet 206 in the first direction, and an adjacent edge of a turbulence generating element 210 extending from the plane of the zig-zag sheet 206 in a second direction, opposite the first direction. The turbulence generating element 210 extending from the plane of the zig-zag sheet 206 in the second, opposite direction, may be positioned on the same or a different turn 208 as the turbulence generating element 210 extending from the plane in the first direction. In the case of two adjacent turbulence generating elements 210 extending in opposite directions and from the same turn 208, the distance X is equal to L1+2·L2−2·L and may approach 0. An opposite side pitch ratio (X/W) is in the range of about 0 to about 50. The approach angle θ formed between each turbulence generating element 210 extending away from the plane of the zig-zag sheet 206 and a fluid flow over the turbulator 200 may be in the range of about 10° to about 45°. In one embodiment, the approach angle is about 27°. The inclination angle of the turbulence generating elements 210 in relation to the plane of the zig-zag sheet 206 may be between about 25° and about 90°. Alternatively, at least a portion of at least one turbulence generating element 210 may have an inclination angle in relation to the plane of the rectangular sheet 206 other than 90°, for instance between 15° and 65°.

In another embodiment, shown in FIG. 16, the zig-zag sheet 206 may be bent about a longitudinal axis such that a first portion of the turns 208 of the zig-zag sheet 206 is arranged at an angle to a second portion, or the remainder of the plurality of turns 208. In one embodiment, the angle between the first portion of the plurality of turns and the second portion of the plurality of turns 208 is about 90°. In another embodiment, the angle between the first portion of the plurality of turns and the second portion of the plurality of turns 208 is about 120°.

Referring now to FIGS. 17-19, the ends 102, 104 of the turbulator 100, 200 may be configured to provide a means for securing the turbulator 100, 200 within the heat exchanger tube 52. In the arrangement shown in FIG. 17, the ends 102, 104 of the turbulator 100, 200 are cut to form a securing element 120. In one embodiment, the securing element 120 is a generally rectangular flap. The securing element 120 is subsequently folded over at both ends 102, 104 of the tube 52 to constrain movement of the turbulator 100, 200 along a longitudinal axis of the tube 52. Alternatively, as shown in FIG. 18, a plurality of smaller, generally triangular securing elements 120, may be formed at the ends 102, 104 of the turbulator 100. These smaller securing elements 120 minimize obstruction to the flow entering and exiting the tube 52, thus reducing pressure drop. Each of these securing elements 120 is configured to contact an interior or exterior wall of the heat exchanger tube 52. These securing elements 120 will support and stabilize the end of the turbulator 100, 200 within the heat exchanger tube 52. The securing elements 120 may be cut and then bent after the plurality of turbulence generating elements 110, 200 are formed. When the turbulator 100, 200 is installed in the tube 52, the second end 104 of the turbulator 100, 200 may be rotated relative to the first end 102 so that the turbulator 100, 200 includes at least one twist. In one non-limiting embodiment, as illustrated in FIG. 20, the second end 104 is rotated 180 degrees about the longitudinal axis relative to the first end 102. Inclusion of at least one twist in the turbulator 100, 200 stabilizes the turbulator 100, 200 by centering the sheet 106, 206 within the tube 52.

Inclusion of a turbulator 100, 200 in a heat exchanger tube 52 improves the heat transfer efficiency of the heat exchanger tube 52. By inserting the turbulence generating elements 110, 210 into the heating fluid flow, a large scale disturbance is formed adjacent an edge of each turbulence generating element 110, 210. This disturbance effectively transports fluid from the center of the heat exchanger tube 52 to the heat transfer surface at the wall of the heat exchanger tube 52 with a relatively small increase in pressure drop. The turbulence generating elements 110, 210 are effective in improving the heat transfer in both dry operating conditions as well as condensing conditions, and may be consequently applied within the primary heat exchanger 12 or the condensing heat exchanger 8. The turbulator 100, 200 may be formed through a simple manufacturing process, and the parameters of the turbulator 100, 200 including size, shape, and number of turbulence generating elements 110, 210 may be easily adapted for various applications.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

1. A heat exchanger comprising: a plurality of heat exchanger tubes, wherein a first fluid flows through each heat exchanger tube and a second fluid flows around an exterior of each heat exchanger tube; and a turbulator disposed in one of the heat exchanger tubes and extending at least a portion of a length of the heat exchanger tube, the turbulator including a generally flat rectangular sheet having a plurality of integrally formed turbulence generating elements extending from a plane of the rectangular sheet into the first fluid flow, wherein a disturbance is generated in the first fluid flow adjacent each turbulence generating element.
 2. The heat exchanger according to claim 1, wherein the plurality of turbulence generating elements are uniform in size and shape.
 3. The heat exchanger according to claim 1, wherein the plurality of turbulence generating elements are triangular in shape.
 4. The heat exchanger according to claim 1, wherein the plurality of turbulence generating elements are one of rectangular, oval, racetrack and semi-circular in shape.
 5. The heat exchanger according to claim 1, wherein the plurality of turbulence generating elements are aligned about a longitudinal axis of the rectangular sheet.
 6. The heat exchanger according to claim 1, wherein at least one of the turbulence generating elements extends from the plane of the rectangular sheet in a first direction, and at least one of the turbulence generating elements extends from the plane of the rectangular sheet in a second, substantially opposite direction.
 7. The heat exchanger according to claim 1, wherein a width W of at least a portion of a turbulence generating element is in the range of about 4 mm to about 25 mm.
 8. The heat exchanger according to claim 7, wherein each of the plurality of turbulence generating elements has a length L and chord ratio (L/W) in the range of about 1 to about
 5. 9. The heat exchanger according to claim 7, wherein a pitch P extends between adjacent turbulence generating elements extending from the plane of the rectangular sheet in the first direction, and a same side pitch ratio (P/W) is in the range of about 5 to about
 100. 10. The heat exchanger according to claim 7, wherein a distance X is defined between a first turbulence generating element extending from the plane of the rectangular sheet in a first direction and a second turbulence generating element extending from the plane of the rectangular sheet in a substantially opposite direction, and an opposite side pitch ratio (X/W) is in the range of about 0 to about
 50. 11. The heat exchanger according to claim 1, wherein an approach angle is formed between the chord line of the turbulence generating element and an airstream velocity vector and the airstream velocity vector, the approach angle being in the range of about 10 degrees to 90 degrees.
 12. The heat exchanger according to claim 1, wherein at least one of the plurality of turbulence generating elements has an inclination angle other than 90 degrees.
 13. The heat exchanger according to claim 1, wherein a first end of the turbulator includes at least one securing element that supports the turbulator within the heat exchanger tube.
 14. The heat exchanger according to claim 1, wherein a first end of the turbulator is rotated relative to a second end of the turbulator about a central longitudinal axis such that the turbulator includes at least one twist.
 15. A condensing furnace comprising: a heat exchanger having an inlet and an outlet, wherein a first fluid flows through the heat exchanger and a second fluid flows around an exterior of the heat exchanger; and a turbulator positioned within the heat exchanger, the turbulator extending at least a portion of a length of the heat exchanger, the turbulator including: a generally flat rectangular sheet; and a plurality of turbulence generating elements formed integrally with the rectangular sheet and extending from a plane of the rectangular sheet into the first fluid flow, such that a disturbance is created in the first fluid flow adjacent each turbulence generating element.
 16. A heat exchanger comprising: a plurality of heat exchanger tubes, wherein a first fluid flows through each heat exchanger tube and a second fluid flows around an exterior of each heat exchanger tube; and a turbulator disposed in one of the heat exchanger tubes and extending at least a portion of a length of the heat exchanger tube, the turbulator including a generally flat sheet of material having a substantially non-linear contour configured to interrupt a flow of the first fluid through the heat exchanger tube.
 17. The heat exchanger according to claim 16, wherein the turbulator is bent about a longitudinal axis thereof.
 18. The heat exchanger according to claim 16, wherein the sheet of material has a general zig-zag shape and includes a plurality of opposing turns.
 19. The heat exchanger according to claim 18, wherein the generally zig-zag shape is formed from a plurality of staggered generally linear sections connected by a plurality of angled sections, each successive angled section being oriented in a first direction opposite a second direction of a preceding angled section.
 20. The heat exchanger according to claim 18, wherein the turbulator includes a plurality of turbulence generating elements extending from a plane of the flat sheet of material into the first fluid flow, each of the plurality of turbulence generating elements being configured to create a disturbance in the first fluid.
 21. The heat exchanger according to claim 20, wherein the plurality of turbulence generating elements are formed in the opposing turns of the flat sheet.
 22. The heat exchanger according to claim 21, wherein the plurality of turbulence generating elements are triangular in shape.
 23. The heat exchanger according to claim 21, wherein at least one of the turbulence generating elements extends from the plane of the sheet of material in a first direction, and at least one of the turbulence generating elements extends from the plane of the sheet of material in a second, substantially opposite direction.
 24. The heat exchanger according to claim 21, wherein a width W of at least a portion of a turbulence generating element is in the range of about 4 mm to about 25 mm.
 25. The heat exchanger according to claim 24, wherein the plurality of turbulence generating elements have a chord ratio (L/W) in the range of about 1 to about
 5. 26. The heat exchanger according to claim 24, wherein a pitch P extends between adjacent turbulence generating elements extending from the plane of the sheet of material in the first direction, and a same side pitch ratio (P/W) is in the range of about 2 to about
 100. 27. The heat exchanger according to claim 24, wherein a distance X is defined between a first turbulence generating element extending from the plane of the rectangular sheet in a first direction and from a second turbulence generating element extending from the plane of the rectangular sheet in a substantially opposite direction, and an opposite side pitch ratio (X/W) is in the range of about 0 to about
 50. 28. The heat exchanger according to claim 20, wherein an approach angle is formed between the chord line of the turbulence generating element and an airstream velocity vector and the airstream velocity vector, the approach angle being in the range of about 10 degrees to 90 degrees.
 29. The heat exchanger according to claim 20, wherein at least one of the plurality of turbulence generating elements has an inclination angle other than 90 degrees.
 30. The heat exchanger according to claim 16, wherein a first end of the turbulator includes at least one securing element configured to support the turbulator within the heat exchanger tube.
 31. A condensing furnace comprising: a heat exchanger having an inlet and an outlet, wherein a first fluid flows through the heat exchanger and a second fluid flows around an exterior of the heat exchanger; and a turbulator positioned within the heat exchanger, the turbulator extending at least a portion of a length of the heat exchanger, the turbulator including a generally flat sheet of material having a substantially non-linear contour configured to interrupt a flow of the first fluid through the heat exchanger tube. 